Subzero: Assemble calls to constant addresses.

src/IceFixups.cpp

 //===- subzero/src/IceFixups.cpp - Implementation of Assembler Fixups -----===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the AssemblerFixup class, a very basic
 // target-independent representation of a fixup or relocation.
 //
 //===----------------------------------------------------------------------===//
 
 #include "IceFixups.h"
 #include "IceOperand.h"
 
 namespace Ice {
 
+const Constant *AssemblerFixup::NullSymbol = nullptr;
+
 RelocOffsetT AssemblerFixup::offset() const {
+  if (isNullSymbol())
+    return 0;
   if (const auto CR = llvm::dyn_cast<ConstantRelocatable>(value_))
     return CR->getOffset();
   return 0;
 }
 
 IceString AssemblerFixup::symbol(const GlobalContext *Ctx) const {
   std::string Buffer;
   llvm::raw_string_ostream Str(Buffer);
   const Constant *C = value_;
+  assert(!isNullSymbol());
   if (const auto CR = llvm::dyn_cast<ConstantRelocatable>(C)) {
     if (CR->getSuppressMangling())
       Str << CR->getName();
     else
       Str << Ctx->mangleName(CR->getName());
   } else {
     // NOTE: currently only float/doubles are put into constant pools.
     // In the future we may put integers as well.
     assert(llvm::isa<ConstantFloat>(C) || llvm::isa<ConstantDouble>(C));
     C->emitPoolLabel(Str);
   }
   return Str.str();
 }
 
 void AssemblerFixup::emit(GlobalContext *Ctx) const {
   Ostream &Str = Ctx->getStrEmit();
+  // TODO(jvoung): Not yet clear how to emit a relocation against
+  // the null symbol.
+  assert(!isNullSymbol());
   Str << symbol(Ctx);
   RelocOffsetT Offset = offset();
   if (Offset)
     Str << " + " << Offset;
 }
 
 } // end of namespace Ice